1. Field of the Invention
This invention relates to an optical system having image deflecting means, and particularly to an optical system having image deflecting means suitable for a telescope, binoculars, a photographing system or the like wherein a variable angle prism having its vertical angle variable is provided in a lens system and an image is deflected by the variable vertical angle prism to thereby stabilize the vibration of the image caused by vibration or the like.
2. Related Background Art
When an object is observed from on a running vehicle or the like by means of an optical system such as a telescope, the vibration of the vehicle is transmitted to the optical system to cause vibration (blurring) to be created in an image. There have heretofore been proposed various optical systems having image deflecting means wherein a plane parallel plate or a variable angle prism is disposed in an optical system to thereby correct the vibration of the image at such time.
For example, an optical system in which a variable angle prism is utilized to correct the vibration of an image is proposed in Japanese Patent Publication No. 56-21133. In this publication, liquid or a transparent elastic member is enclosed between two plane parallel glass plates and the angle formed by the two plane parallel plates is made variable to thereby correct the vibration of the image.
Besides this, this publication proposes a photographing system in which a plano-convex lens and a plano-concave lens each having a curvature are slid between spherical surfaces to thereby make the angle formed by the opposed planar surfaces variable and correct the vibration of an image.
Generally, where a variable angle prism is disposed forwardly of or in a lens system to correct the vibration of an image, when the vertical angle of the variable angle prism is given a certain degree of angle, the deflection of the image and chromatic aberration of eccentric magnification are created by the color dispersion of the prism.
An optical system in which the chromatic aberration of eccentric magnification at such time is corrected well by appropriately selecting the material of the variable angle prism is proposed, for example, in Japanese Laid-Open Patent Application No. 1-178916.
Generally, when an attempt is made to vary the vertical angle of a variable angle prism to thereby correct the vibration of an image, the vertical angle of the prism is enlarged and chromatic aberration of eccentric magnification increases proportionally, and the quality of the image becomes deteriorated. It is very difficult to correct the chromatic aberration of eccentric magnification at this time by an optical system including a variable angle prism while contriving the simplification of the lens construction, and unavoidably the lens construction tends to become complicated.
For example, in binoculars using a pair of optical systems, use must be made of a simple lens construction and therefore, when image deflecting means comprising a variable angle prism is applied to it to thereby correct the vibration of an image, chromatic aberration of eccentric magnification poses a great problem.